1. Field of Invention
The present invention relates to a technical field of electro-optical devices such as liquid crystal devices, and electronic apparatuses. The present invention also relates to a technical field of an electrophoresis device, such as an electronic paper, an EL (electroluminescent) device, and a device using an electron emission element (a field emission display and a surface-conduction electron-emitter display).
2. Description of Related Art
In the related art, an electro-optical device, such as a liquid crystal device capable of displaying an image, in which an electro-optical material, such as liquid crystal, is interposed between a pair of substrates and light is transmitted so as to pass through the substrates and the electro-optical material, is disclosed. “Displaying the image” is realized, for example, by changing the state of an electro-optical material in each pixel to change the transmittance ratio of light and by causing light with different gray scale levels to be sensed in each pixel.
As such an electro-optical device, an active-matrix driven electro-optical device has been proposed which includes, on one of the pair of substrates, pixel electrodes arranged in a matrix, scanning lines and data lines positioned to thread through the pixel electrodes, and TFTs (thin film transistors) as pixel switching elements. According to the electro-optical device capable of being active matrix driven, the TFTs are provided to control conduction between the pixel electrodes and the data lines. The TFTs are electrically connected to the scanning lines and the data lines. Therefore, it is possible to control the turning on and off of the TFTs through the scanning lines and to apply image signals received through the data lines to the pixel electrodes, that is, to change the transmittance ratio of light in each pixel when the TFTs are turned on.
According to the above-mentioned electro-optical device, the above-mentioned various components are formed on one substrate. However, when the components are expanded two-dimensionally, the components occupy a large area, and a pixel aperture ratio, that is, a ratio of a region through which light passes to the entire surface of the substrate may decrease. Therefore, even in the related art, a method of forming the above-mentioned various components three-dimensionally, that is, a method of laminating the various components by interposing interlayer insulating layers is adopted. More specifically, the TFTs and the scanning lines, functioning as gate electrode films of the TFTs, are formed on the substrate. The data lines are formed on the TFTs and the scanning lines. The pixel electrodes are formed on the data lines. According to such a construction, it is possible to enhance the pixel aperture ratio by appropriately arranging the various components as well as to miniaturize the electro-optical device.
It is natural and essential for the electro-optical devices to demand a high quality display, and moreover, miniaturization, high accuracy, and high frequency driving. In order to meet the demands, many technical problems have to be solved. Specifically, for example, there is a problem of the so-called light leakage current which is generated when light enters the semiconductor layers constituting the aforementioned TFTs. The light leakage current is one of the obstacles to the high quality image display and the high frequency driving. Therefore, light-shielding devices are necessary for the semiconductor layers. Furthermore, for the purpose of implementing the electro optical apparatus with high contrast, storage capacitors, that is, condensers are sometimes provided to electrically connect the TFTs to pixel electrodes, and the capacitance value of the storage capacitor should be as large as possible. However, the implementation is difficult because of the complexity in the laminated structure and the problems associated with the aperture ratio as described above. Furthermore, much attention has to be given to the liquid crystal, which is an example of the electro optical materials, in order to avoid any unnecessary external disturbance from being added to the alignment states of the liquid crystal molecules.
Like this, although there are many problems to be addressed, it is believed that the aforementioned problems have to be totally considered and the overall measures have to be taken to achieve high quality image display by addressing the aforementioned problems in relation to miniaturization, high accuracy, and high frequency driving in the electro optical apparatus.